1. Field of the Invention
The present invention is related to differential drivers and, in particular, to methods and systems for an improved method of correcting the variation of Voltage Output Differential (VOD) due to process and temperature variations in differential drivers.
2. Description of Related Art
A differential driver is an electronic device, commonly an integrated circuit, which is used to drive complementary signals that are carried on pairs of conductors. Differential drivers are commonly used for driving lines that may interconnect, for example, integrated circuits, peripheral devices, or traces. Differential drivers are also commonly used in clock circuits and in Multipoint Low-Voltage Differential Signaling (MLVDS) applications. MLVDS systems provide high-speed, low-power signal processing for such applications as wireless base stations, Digital Subscriber Line Access Multiplexers (DSLAMs), handheld consumer electronics, and other telecommunications equipment.
Differential signals are commonly referenced to each other, rather than to a source of ground potential or other reference voltage. In some systems, one signal (i.e., a first voltage between the two conductors) may be referenced as “high” or “positive” and the other signal (i.e., a second voltage between the two conductors) as “low” or “negative.”
The average voltage of a differential signal defines that signal's “common-mode” voltage. To ensure proper operation of the differential input and output drivers in a high-speed link, the voltage swing (i.e., the amount that a particular voltage varies over time) of each of the differential signals and the common-mode voltage of each signal should remain within certain prescribed ranges.
In the field of differential drivers, the Output Differential Voltage (VOD) is typically defined by driving a constant output current through an external load resistor. The resistor in such a system typically has a large range of resistance—changing plus or minus 20% with process and temperature. The result of such high variation in the system can be an unstable VOD that can greatly reduce the performance of the output driver by, for example, reducing the noise immunity of the system.
Therefore, there is a need for methods and systems for an improved variation in output currents, and consequently the Voltage Output Differential (VOD), in differential drivers.